The purpose of the research is to continue our investigation of the development of search strategies. Several interwoven goals will be addressed. These include (a) investigating the development of comprehensive search strategies, in order to complement our earlier work on selective search strategies. In this we are particularly interested in investigating the development of children's abilities to plan ahead in order to efficiently search all locations. We hypothesize that comprehensive search develops from sighting-based to more planful search procedures, and propose experiments to examine and account for this development. A further hypothesis is that the searcher's conception of distance is central to his/her ability to plan search paths of various sorts. This necessitates (b) investigating children's developing conceptions of distance and length. Surprisingly, little is known about this crucial conceptual development. Furthermore, in our analysis of search ability the notion of search efficiency is a key construct. We therefore propose to carefully examine the development of search efficiency. To do so requires expansion of past research to new sorts of search problems. Specifically, we extend our focus to include studies of children's developing skills at solving search problems (c) which involve detecting the object of search in order to find it, and (d) which require whereabouts rather than finding strategies. Finally (e) we propose to further investigate the early origin of search skills in infants and toddlers. Our overall aim is to advance toward a general model of human search ability and its development. This should in turn advance our understanding of large-scale spatial cognition as well as the development of problem-solving more generally.